Method for determining the concentration of hydrogen peroxide in a process stream and a spectrophotometric system for the same

ABSTRACT

The present invention is directed to a method for determining the concentration of hydrogen peroxide in a chemical process stream which may include interfering components. Still further, this invention is directed to a method and apparatus for the on-line, automated determination and control of hydrogen peroxide in a process stream.

DESCRIPTION OF THE INVENTION

The present invention is directed to a method for determining theconcentration of hydrogen peroxide in a chemical process stream. Moreparticularly, the present invention is directed to a method fordetermining the concentration of hydrogen peroxide in a chemical processstream which may include interfering components. Still further, thisinvention is directed to a method and apparatus for the on-line,automated determination and control of hydrogen peroxide in a processstream.

Hydrogen peroxide has become a common bleaching agent that is used in awide variety of commercial process streams. The application of hydrogenperoxide in commercial bleaching processes has lessened theenvironmental impact of prior chlorine based bleaching processes.Hydrogen peroxide has become a staple bleaching agent for use, forexample, in pulp and paper manufacture and in textile manufacture.Control of the concentration of hydrogen peroxide used in thesebleaching processes can eliminate issues associated with incompletebleaching or economic waste. Insufficient hydrogen peroxide results inincomplete bleaching, while excess hydrogen peroxide results in waste.

During pulp manufacture, for example, insufficient residual peroxide canlead to brightness reversion. On the other hand, excess hydrogenperoxide is expensive and results in waste. Therefore, monitoring thehydrogen peroxide concentration in a pulp stream during the pulpbleaching process can result in the

The presence and concentration of hydrogen peroxide can be determinedusing a spectroscopic determination, for example spectroscopy in thevisible, ultraviolet (UV) and IR ranges. However, when othercompositions are present, these compositions may result in interferencemaking it difficult, or impossible, to measure hydrogen peroxidecontent. While some interfering compositions can be successfullyremoved, many can not, and the removal process may be difficult,expensive, or time consuming.

The present invention provides a method for determining the presence andconcentration of hydrogen peroxide in a process stream, despite thepresence of these interfering compositions. According to one embodimentof the present invention, the concentration of hydrogen peroxide can bemeasured quickly and easily. According to another embodiment of theinvention, the hydrogen concentration can be used to provide anautomated response which adjusts the amount of the hydrogen peroxide inthe process.

The present invention allows for either on-line or off-line measurementof the concentration of hydrogen peroxide in a process stream. Accordingto both of these embodiments of the invention, the hydrogen peroxidecontent may be measured in real time making it possible to modify andcontrol the hydrogen peroxide content and thus, control the bleachingprocess.

According to one embodiment of the present invention, the use of anisosbestic point and the application of a dual wavelength method make itpossible to eliminate the spectral interference of interferingcompounds. An isosbestic point refers to a wavelength at which a set ofsolutions with different compositions have the same absorptivity.

The present invention can be used to evaluate and control the hydrogenperoxide content in process streams which have heretofore been difficultto evaluate due to the presence of spectral interfering compositions.Appropriate process streams for use with the present method will bereadily apparent to the skilled artisan. A non-exhaustive list ofprocess streams includes pulp bleaching streams, textile bleachingstreams, wastewater treatment streams, and other chemical streams thatrequire hydrogen peroxide. While the present invention will be describedgenerally with respect to a pulp bleaching stream, application andadaptation of this method and apparatus to other hydrogen peroxidecontaining process streams will be readily apparent to the skilledartisan.

According to one embodiment, the method and apparatus of the presentinvention are used to determine the hydrogen peroxide concentration in apulp bleaching stream. In the area of pulp process streams, the use ofhydrogen peroxide relates to the production of total chlorine free pulps(TCP). Spectral interfering compounds found in pulp bleaching streamsinclude dissolved lignin. Dissolved lignin is not a single composition,per se, but is a combination of related compounds which have similarspectral properties.

Much of the dissolved lignin can be precipitated from the bleachingstream in an acidic medium. However, acidifying the medium does notremove all of the lignin and therefore, does not eliminate all of thespectral interference created by the dissolved lignin. While the methodof the present invention can used without removing any of the dissolvedlignin, it can also be used to determine the hydrogen peroxide contentfor a stream where some of the lignin has been eliminated. The dualwavelength method allows for the spectral interference of dissolvedlignin from the pulp bleaching stream to be negated in the absorptionmeasurement. Specifically, the isosbestic point allows one to accountfor the spectral interference from dissolved lignin in the processstream.

Reference will now be made in detail to the embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an off-line apparatus for hydrogen peroxidedetermination through UV spectroscopy.

FIG. 2 illustrates an apparatus for on-line hydrogen peroxidedetermination through UV spectroscopy.

FIG. 3 plots the absorption of molybdate versus the concentration ofperoxymolybdate and illustrates the isosbestic point.

FIG. 4 plots the absorption of molybdate at 350 nm versus aconcentration range of hydrogen peroxide from 0 to 0.12 g/L under amolybdate concentration of 3.2 mmol/L.

FIG. 5 plots absorbance versus the volume of the oxygen delignificationliquor added in a 5 mL, 3.2 mM molybdate solution and illustrates theeffect of dissolved lignin on absorption.

DETAILED DESCRIPTION

The present invention is directed to a method for determining hydrogenperoxide concentration in a chemical process stream in the presence ofat least one interfering compound. At least one interfering compoundrefers to one or more compounds or complexes with spectral interference.More particularly, spectral interference refers to interference whichcan be measured in the visible, infrared, and ultraviolet ranges throughspectrophotometry. According to another embodiment of the invention, thechemical process stream to be evaluated for hydrogen peroxide contentcontains multiple interfering compounds. While the invention will begenerally described with reference to a UV system, application of theinvention to the visible and IR ranges would be readily apparent to theskilled artisan.

According to one embodiment of the present invention, the concentrationof hydrogen peroxide can be determined using a UV spectrophotometrictechnique based on the reaction of molybdate and hydrogen peroxide thatresults in a UV absorbing peroxymolybdic complex. Any molybdate salt canbe used to introduce the molybdenum to the sample. The most commonlyused molybdenum salt is ammonium molybdate; however, other forms ofmolybdate salt, such as but not limited to, potassium molybdate, sodiummolybdate, or chromium molybdate can be used.

First, a sample is taken from the process stream for analysis. Thesample may be removed from the stream or accessed, by, for example, anautomated sensor. This composition of the sample should berepresentative of the overall composition of the chemical stream, orthat section of the process stream that is of interest. One skilled inthe art will recognize that the sample can be taken at any point in theprocess at which it is decided to measure the hydrogen peroxide. Forexample, hydrogen peroxide content can be measured at the end of theprocess to ascertain the residual peroxide content prior to disposal ofany portion of the bleaching stream.

The size of the sample can vary and will be readily apparent to theskilled artisan based upon the anticipated content of hydrogen peroxideand the measurement apparatus that is being used. When using an off-linemethod, if the anticipated concentration of hydrogen peroxide is low,then a larger sample should be removed from the process stream toincrease the amount of hydrogen peroxide present in the sample.Likewise, if the anticipated concentration of hydrogen peroxide is high,then a smaller sample should be removed from the process stream.

When using an on-line process, the concentration of hydrogen peroxideshould fall within a measurable range. A measurable range ofconcentrations includes the range recognized by a standardspectrophotometer, i.e., the range in which the concentration is not toolow to be detected by the spectrophotometer nor is the sample tooconcentrated to be measured. If the sample extracted is too concentratedor too dilute, then the sample or sample size would need to be modified.Appropriate methods for modification would be readily apparent to oneskilled in the art, and would include diluting or concentrating thesample, respectively.

The sample can be removed from the process stream, for example, in anoff-line determination. In an off-line measuring system, the sample istaken from the process stream using any art recognized method,including, but not limited to a valve, tap, or spout. In an off-linemeasuring system, the sample is usually taken at the end of thebleaching process; however, the sample can be taken at any point in theprocess at which it is decided to measure the concentration of hydrogenperoxide.

According to one embodiment of the present invention, the sample shouldbe kept at a constant temperature after the sample is removed from thechemical process stream. The temperature at which the sample isprocessed is not critical and can be any temperature in the rangebetween which the sample freezes or vaporizes. According to oneembodiment of the present invention, the sample is cooled. According toanother embodiment, the sample is maintained at a constant cooledtemperature. Appropriate cooling methods and systems will be readilyapparent to the skilled artisan. Any cooling mechanism can be used withthe present invention and the cooling system can preferably maintain aconstant temperature.

The molybdate solution is added to the sample. The amount of molybdatesolution necessary will be based upon the sample size and anticipatedconcentration of hydrogen peroxide. Thus, one skilled in the art could,based upon knowledge of the stream to be tested and the known reactionof hydrogen peroxide and molybdate to form the colorimeticperoxymolybdic acid complex, select an appropriate amount andconcentration of molybdate solution. According to one embodiment of thepresent invention, an excess of molybdate solution is added to thehydrogen peroxide containing stream or sample. The addition of themolybdate results in its reaction with the hydrogen peroxide to form aperoxymolybdic acid compound. Through the addition of an excess ofmolybdate, the amount of peroxymolybdic acid complex formed in theaqueous solution is substantially proportional to the amount of hydrogenperoxide in the sample compound.

The amount of molybdate solution that should be added to the sampledepends upon the anticipated concentration of hydrogen peroxide in thesample and the size of the sample taken from the process stream. Themolybdate solution added to the sample creates an independent absorptionin the same spectrum as the peroxymolybdate complex. Therefore,measuring the concentration of hydrogen peroxide requires that thespectral interference from the molybdate be negated. Thus, according toone embodiment of the present invention, the molybdate solution is addedat a concentration that is below the saturation level. Thus, while anyamount of excess molybdate can be used, since the baseline absorption ofthe molybdate can interfere with the measurement of the concentration ofthe hydrogen peroxide, the concentration of the molybdate solutionshould not go too high, i.e., about the saturation level.

Regardless of which system of measurement is chosen, the instrument mustbe calibrated before the absorption of the sample can be measured. Theinstrument can be calibrated with any known reagent for calibration thatis available from commercial sources and would be readily apparent to askilled artisan.

FIG. 1 illustrates one embodiment of the present invention. FIG. 1illustrates an off-line system for determining the concentration ofhydrogen peroxide. According to this embodiment, a sample [40] is firstremoved from a chemical process stream (not shown). After removal, thesample [40] is placed in a receptacle with stirring. According to theembodiment shown in FIG. 1, the sample is placed in a beaker [50] andstirring is undertaken with a stirring bar [50] and a magnetic stirringmeter [55]. Stirring can be carried out with any art recognized stirringmeans. Appropriate stirring systems will be readily apparent to theskilled artisan.

According to the embodiment shown in FIG. 1, a net filter [60] issubmerged in the solution, allowing the sample to be removed from thebeaker by a pump [70]. The filter must be used to prevent the fiber [65]present in the process sample from entering the pump.

According to the embodiment shown in FIG. 1, the sample is then bepassed through a flow cell [75] that is illuminated from behind by alight source

-   -   to a spectrophotometer [85]. The spectrophotometer then measures        the absorption of the sample from the light stream at two        wavelengths, e.g., approximately 297 nm and approximately 350        nm.

Any art recognized spectrophotometer can be used. The spectrophotometerchosen should be capable of measuring an aqueous solution in a range ofabout 250–500 nm. Appropriate spectrophotometers for use in the presentinvention includes, for example HP-8452 and other variations that wouldbe readily available to one skilled in the art. The photometric arraydetector [90] is an integral part of current commercialspectrophotometers.

After the sample spectral absorbencies have been measured, thisinformation should be transmitted to a computer [95] for the calculationof the amount of hydrogen peroxide in the chemical process stream.Adjustments in hydrogen peroxide content can be controlled manuallybased upon this information or may be fed to a control system foradjusting the hydrogen peroxide addition amounts. If the calculationshows that the concentration of hydrogen peroxide in the process streamis too high, the intake amount of the hydrogen peroxide should bereduced.

FIG. 2 illustrates another embodiment of the present invention. Asdepicted in FIG. 2, an on-line detection system may be used to sampleand evaluate a chemical process stream [5]. The on-line system isintegrated directly into the manufacturing process and is capable ofeither sampling upon command or continuously.

According to one embodiment of the present solution, after the sample isremoved from the process stream, the sample is transferred to a coolingchamber [10]. Appropriate cooling methods and systems will be readilyapparent to the skilled artisan. Any cooling mechanism that can cool thesample, preferably to a constant temperature, can be used. According tothe embodiment shown in FIG. 2, once the sample has been cooled, thesample is removed from the cooling chamber by a pump [15] that removesthe sample to the sample loop of an injection valve [20]. Any pump thatis capable of removing the removing the sample from cooling chamber andtransporting it to the injection valve can be used. Appropriate pumpswill be readily apparent to a skilled artisan.

According to one embodiment of the present solution, the sample in thesample loop can be injected into the molybdate solution. Appropriateinjection valves will be readily apparent to the skilled artisan. Afterthe sample is combined with the molybdate solution, the sample istransferred to a flow cell [25] by a second pump [15], where it isirradiated with a light source [30] to a spectrophotometer [35]. Thespectrophotometer should then measure the absorption of the sample fromthe light stream at two wavelengths, such as 297 nm and 350 nm. Astandard spectrophotometer should be used, such as the HP-8452 and othervariations that would be readily available to one skilled in the art.The spectrophotometer should be chosen based upon the analysis to beundertaken on the stream to be evaluated and may be chosen from aspectrophotometer capable of measuring the absorption of an aqueousstream in ultraviolet, visible and infrared spectrophotometry.

After the measurement of the sample has been taken, this informationshould be transmitted from the spectrophotometer to a computer [95].This computer can be connected to the hydrogen peroxide dosing systemthat controls the amount of hydrogen peroxide that is added to theprocess stream. By concurrently automating the dosing system and thehydrogen peroxide analysis, a closed-loop system for modifying theamount of hydrogen peroxide added to the stream can be created. Thus,the concentration of hydrogen peroxide can be kept within a desiredrange.

After the sample passes through the flow cell and the absorptionmeasurements have been taken, the sample can be discarded.

Another embodiment of the present invention involves the method ofmeasuring the absorption of the chemical process stream at twowavelengths. The absorption of the sample should be taken at theisosbestic point and at a wavelength where the concentration of hydrogenperoxide can be measured. Still further, the present invention involvesmeasuring the absorption of the chemical process stream at between about300 and about 450 nm and at between about 292 and about 302 nm. Thesewavelengths should be compared to eliminate spectral interference ofadditional compounds dissolved in the process stream. This comparison isdone using the dual wavelength method, which will be discussed infra.

The absorption of the sample should be taken at two wavelengths. Theisosbestic point occurs at the wavelength in which the absorption ofdifferent compositions is constant regardless of a change inconcentration. The isosbestic point for hydrogen peroxide and molybdatesystems occurs between 292 and 302 nm.

Molybdate ions exhibit a strong spectral absorption in the UV range, asshown by FIG. 3. The range of the absorption overlaps the rangeexhibited by the peroxymolybdate complex; therefore, measuring theconcentration of hydrogen peroxide requires the negation of the spectralinterference from the molybdate. To eliminate spectral interference frommolybdate, the second measurement should be taken at a wavelength wherethe absorption of molybdate can be negated, which occurs at wavelengthslonger than 330 nm.

Once the measurements have been made, the measured absorptions must becompared to eliminate the spectral effect of interfering compounds foundin the chemical stream. The dual wavelength method allows for the strongspectral interference from dissolved lignin in the process to be removedand the concentration of hydrogen peroxide to be determined. The dualwavelength method is demonstrated by the following example:$C = {\frac{k_{1}}{V_{sample}}\left\lbrack {{k_{3}A_{X}} - {k_{2}\left( {{k_{3}A_{Y}} - A_{Y}^{o}} \right)} - A_{X}^{o}} \right\rbrack}$

In this equation, C is the concentration of hydrogen peroxide (in g/L)and V_(sample) is the sample volume (mL) added into the molybdatesolution. The variables A_(x) and A_(y) represent the absorption ofperoxymolybdate complex and the isosbestic point, respectively. Thevariables A⁰ _(x) and A⁰ _(y) represent the absorption measurements ofthe molybdate solution before the sample was added at X and theisosbestic point, respectively. The calibration constant, k₁, can beobtained by plotting the absorption of molybdate at 350 nm against aconcentration range of hydrogen peroxide in a molybdate solution, asdemonstrated by FIG. 4. The correction factor k₂ can be obtained bycalculating the average ratio of A_(x)/A_(y), as demonstrated by TableII infra. The dilution factor, k₃, is used to correct for the dilutionof the testing solution when the bleaching stream sample is added intothe molybdate solution. If the volume of the molybdate solution wasV_(molyb), then the following equation can be used to calculate k₃:$k_{3} = \frac{V_{molyb}}{V_{molyb} + V_{sample}}$

Another embodiment of the present invention involves the on-linedetermination of the concentration of hydrogen peroxide in a chemicalprocess. This embodiment involves a means for removing the sample fromthe chemical process stream; means for determining the absorption of thesample; and means for determining the concentration of hydrogen peroxidein said sample. Means for removing the sample can include any meansrecognized by one skilled in the necessary art, not to be limited by,but including any pump means, which can be injection, vacuum pumps, andany other pump that will be readily apparent to a skilled artisan.

EXAMPLE

A 3% of hydrogen peroxide, analytical grade, was used as standard forthe calibration obtained from Aldrich Ref. 32. 338-1. The amount ofhydrogen peroxide in the standard solution was obtained by titrationusing the KCL method. A color agent, 2 mmol/L (NH₄)₂MoO₄ solution wasprepared by dissolving 0.10 grams of (NH₄)₂MoO₄ in 250 mL 0.5 M H₂SO₄.

The hydrogen peroxide content in a bleaching solution or pulp slurry wasdetermined using a titration method known as the KCL Method. A sample ofpulp was obtained from the discharge of a peroxide tower prior toneutralization of the discharge with SO₂ and the consistency of the pulpsample was determined. A sufficient sample of the pulp was then placedin a Buchner and approximately 100 mL of effluent was collected.Twenty-five mL. of the effluent was pipetted into a 250 mL Erlenmeyerflask. Approximately 10–15 mL of 25% H₂SO₄, 5 mL KI solution, and 3drops of saturated ammonium molybdate solution were added to the flask.The sample was then titrated using 0.1N thiosulfate until the solutiondemonstrated a pale yellow color. Once the pale yellow color appeared,ten mL of starch solution purchased from Aldrich Ref. 17. 993-0, wasadded to the sample until the blue color disappeared.

Five sample liquors, three samples from the beginning of the process,shortly after the hydrogen peroxide was introduced, and two samples fromthe end of the process, after bleaching, were taken. A sample liquor wasalso taken from the end of the oxygen delignification process, withoutthe addition of hydrogen peroxide, for use in testing the effect of thedissolved lignin.

The starting pressure of oxygen applied to the process was 60 psi. Thestarting liquor contains 1.27% sodium hydroxide, 0.05% magnesiumsulfate, and 0.5% hydrogen peroxide and a 10% pulp consistency. Thetotal process was 55 minutes. The pressure of oxygen in the systemcontinuously decreased to 0 psi atmospheres at the end of the process.The reaction temperature was kept constant at 700° C. A sample liquorfrom the end of the oxygen delignification process, without addinghydrogen peroxide, was used for the dissolved lignin effect testing.

A spectrophotometer, the HP-8452, Hewlett-Packard, now AgilentTechnologies, CA, USA, equipped with a 1-cm cell was used to conduct theexperiment. The instrument was calibrated by preparing a set of standardsolutions, by adding 2, 4, 8, 12, 16, and 20 μL of standard hydrogenperoxide solution (3%) in a 5 mL ammonium molybdate solution. Theabsorption of each solution was measured at 350 nm using the 1-cm cell.Distilled water was used as a blank in the UV measurement.

Five samples, in three sample sizes, were taken from the preparedbleaching process liquors by micro-syringe. Two samples contained 500μL, one sample contained 100 μL, and two samples contained 10 μL. Eachof these samples were added to the 5 mL molybdate reaction solution andstirred by hand.

The resulting solutions were filtered and their absorbencies weremeasured at wavelengths of 297 nm and 350 nm. FIG. 3 is a graphicalrepresentation of the measured absorbencies of the solutions versustheir wavelengths. The graph reveals that the absorbance of themolybdate solution was constant at 297 nm independent of changes in theconcentration of hydrogen peroxide. This graph also revealed that theabsorption of molybdate was negligible at wavelengths longer than 330nm.

The measured absorption spectral intensity at 350 nm was plotted againsta range of 0 to 0.12 g/L under a molybdate concentration of 3.2 mmol/L,as depicted by FIG. 4. This graph shows a linear relationship betweenthe measured absorption and the known peroxide concentration up to aperoxide concentration up to 0.8 g/L. A nonlinear relationship wasexhibited after a concentration of 0.8 g/L, the nonlinear relationshipthat occurred in concentrations over 0.8 g/L was attributed to theexcess of hydrogen peroxide added to the solution.

The concentration of hydrogen peroxide in the sample was calculatedusing Beer's law. (Beer's law could be used to calculate the hydrogenperoxide content because no interfering components were present in theprepared sample that created spectral interference that needed to beremoved.) The concentration of hydrogen peroxide can be calculated usingthe following equation. $C = {\frac{k_{1}}{V_{sample}}A_{X}}$

where C represents the concentration of hydrogen peroxide (in g/L) and Vrepresents the sample volume (mL) added into the 5 mL molybdatesolution. A₃₅₀ represents the absorption reading at 350 nm. Thecalibration constant, k₁, was calculated from the calibration data shownin FIG. 4.

The method described in this example was validated by the titrationmethod as a reference method. Table I compares the data obtained by thepresent method and the titration method. This comparison indicates thatthe present method provided results similar to the results that wereobtained by the titration method for a sample in the measurableconcentration range of hydrogen peroxide. However, samples withextremely low hydrogen peroxide content were shown to produce a relativedeviation compared to the titration method of up to 10%.

TABLE I Comparisons of measured peroxide in bleaching solution using thereference method and the present method Sample size Hydrogen peroxide,g/L Sample ID (ul) Titration method Present Method RSD, %  1* 500 0.0190.017 −10.5  2* 500 0.051 0.055 7.5 3 100 3.23 3.22 −0.3 4 10 20.8 21.42.9 5 10 31.7 32.4 2.2 *The sample solutions were from an oxygendelignification process, where only small amounts of hydrogen peroxideare used.

The nonlinear curve exhibited in FIG. 4 at concentrations beyond 0.8 g/Lwas caused by the excess of hydrogen peroxide added to the solution,which was not reacted to form the peroxymolybdic complex due to the lackof molybdate. As described in this curve, the molar ratio of peroxide tomolybdate in the peroxymolybdic complex is 1:2.

Dissolved lignin was added to the molybdate solution to study the effectof the dissolved lignin on absorption. FIG. 5 is a graphicalrepresentation of the absorption measured at the two interestwavelengths, 297 nm and 350 nm, versus the volume of the oxygendelignification liquor added in a 5 mL 3.2 mM molybdate solution. Theratio of the absorptions at these two wavelengths, A_(x)/A_(y), wasconstant with a standard deviation of 6.78%, as listed in Table 11,which illustrates in tabular form the spectral absorption contributed bydissolved lignin at the two interest wavelengths. This constantrelationship between the absorptions was found to be independent of theamount of lignin added. Therefore, it was determined that the spectralcontribution of lignin at 297 nm was used to correct for spectralinterference at 350 nm by lignin.

TABLE II Spectral absorption contributed from dissolved lignin at 297and 350 nm* Sample Net absorbance Net absorbance Ratio of No. at 297 nmat 350 nm A₃₅₀/A₂₉₇ 1 0.0513 0.0193 0.376 2 0.0839 0.0327 0.389 3 0.14640.0513 0.350 4 0.2020 0.0681 0.337 5 0.2541 0.0844 0.332 6 0.3215 0.10570.323 7 0.3573 0.1154 0.323 8 0.4258 0.1384 0.325 9 0.4507 0.1479 0.32810  0.5268 0.1757 0.334 Average 0.342 RSTD 6.78% *An sample liquor fromoxygen delignification process (no hydrogen peroxide) is used in thestudy. The content of dissolved lignin is this sample is 40.3 g/L,10–100 μL sample was added into 5 mL 3.2 mM molybdate solution for thetesting.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

1. A method of determining the hydrogen peroxide concentration of achemical process stream containing at least one interfering componentcomprising: adding to said chemical process stream containing hydrogenperoxide, a molybdate solution, wherein said solution contains an excessof molybdate ions, measuring by UV spectroscopy, the absorption atwavelength at or between about 300 and about 450 nm (Absorption A) andat or between about 292 to about 302 nm (Absorption B); and determiningthe concentration of hydrogen peroxide by comparing the two absorptionmeasurements.
 2. The method according to claim 1, wherein the molybdatesolution has a concentration of less than about 3.2 mmol/L.
 3. Themethod according to claim 1, wherein the absorption (Absorption A) ismeasured between about 330 and 375 nm.
 4. The method according to claim1, wherein the absorption (Absorption 8) is measured at between about294 and 300 nm.
 5. The method according to claim 1, wherein saidchemical process stream is an aqueous stream.
 6. The method according toclaim 4, wherein said chemical process stream is at least one of 4 pulpor paper processing stream, a wastewater stream, or a textile bleachingstream.
 7. The method according to claim 1, wherein the chemical processstream is a pulp stream and the at least one interfering component ischosen from dissolved lignin.
 8. The method according to claim 1,wherein said chemical process stream is a pulp or paper process streamand wherein the stream first is treated in an acidic medium toprecipitated dissolved lignin.
 9. The method according to claim 1,wherein the molybdate solution is produced comprising an ammonium saltof molybdenum.
 10. The method according to claim 1, wherein the twoabsorption measurements are compared by the following equation:$C = {\frac{k_{1}}{V_{\;{sample}}}\left\lbrack {{k_{3}A_{X}} - {k_{2}\left( {{k_{3}A_{Y}} - A_{Y}^{o}} \right)} - A_{X}^{o}} \right\rbrack}$wherein C is the concentration of hydrogen peroxide (in g/L) V_(sample)is the sample volume in (mL), A_(x) and A_(y) represent the absorptionof peroxymolybdate complex and the isosbestic point, respectively,wherein the variables A⁰ _(x) and A⁰ _(y) represent the absorptionmeasurements of the molybdate solution before the sample was added at Xand the isosbestic point, k₁, is a calibration constant, k₂ is acorrection factor, and k₃ is a dilution factor.
 11. The method accordingto claim 1, wherein the concentration of hydrogen peroxide in saidprocess stream is changed in response to said determination.
 12. Anon-line system for measuring hydrogen peroxide concentration of achemical process stream containing at least one interfering componentcomprising: means for removing a sample from said chemical processstream; means for determining the UV adsorption of said sample at leasttwo wavelengths; means for determining the concentration of hydrogenperoxide in said chemical process stream; and a means for introducing amolybdate solution to said sample.
 13. The system according to claim 12,wherein said means for removing a sample is a pump.
 14. The systemaccording to claim 12, further comprising cooling means for cooling saidsample prior to measuring the UV adsorption.
 15. The system according toclaim 12, wherein said means for determining the UV adsorption is a UVspectrometer.
 16. The system according to claim 15, wherein said meansfor determining the UV adsorption further comprises a light source. 17.The system according to claim 16, wherein the sample is passed through aflow cell between said UV spectrometer and said light source.
 18. Thesystem according to claim 12, wherein said means for determining theconcentration of hydrogen peroxide is a computer.
 19. An on-line systemfor measuring hydrogen peroxide concentration of a chemical processstream containing at least one interfering component comprising: meansfor removing a sample from said chemical process stream; means fordetermining the UV adsorption of said sample at least two wavelengths;means for determining the concentration of hydrogen peroxide in saidchemical process stream; and a means for introducing a molybdatesolution to said sample; wherein said means for introducing a molybdatesolution to said sample is an injection valve.